The invention relates to an apparatus and method for leading together several printed webs into a multi-layer web sandwich with a harp formed by the deflection rolls assigned to the individual webs.
As a result of their high speed the printed webs received from the printing machine drag air along with them, as a result of which a laminar stream of air attaches itself to the upper and lower sides of the webs. To the extent that this air is enclosed between the webs as the printed webs come together this results in a swelling of the web sandwich and consequently to a domed web sandwich contour which can lead to inaccuracies as the web sandwich passes over one of the fold formers down-stream of the harp.
For this reason it is, therefore, the object of the present invention to provide a device of the type described above by means of which the inclusion of air between the individual webs can be prevented.
This object is achieved according to the invention by providing in the exit area of the harp a means of deflecting the path of the web sandwich from that of a straight line.
The deflection from the straight line path of the web sandwich leads in an advantageous manner to a very small degree of lapping round the deflection rolls provided in the area of the exit from the harp to produce the desired deflection. As a consequence of this lapping the air which has penetrated between the printed webs is pressed out of them, with the result that the swelling and consequently, the domed web sandwich contour are avoided.
Thus, an S-shaped web sandwich can be expediently provided in the exit area of the harp. Advantageously only two deflection rolls are required which are displaced relative to one another in the running direction of the web sandwich and which slightly overlap each other at right angles to that direction. Nevertheless, the air is reliably expressed from the web sandwich.
In a further development of the superior measures relative to a straight-line web sandwich track the web sandwich deflection rolls can be so arranged expediently that the extent of lapping by the web sandwich amounts to 5 to 15°, preferably 10°. These measures ensure that on the one hand the overlap is sufficient to expel the air reliably from the web sandwich and, on the other hand, with the aid of the friction between the webs, is sufficiently small to avoid speed differences resulting from the overlap. This ensures that there is no loss of tension in the outer webs compared with the inner webs.
A further, particularly preferred development of the superior measures can consist of the fact that the two lowest deflection rolls of the harp are arranged so that relative to one another they are displaced in the running direction of the web sandwich and slightly overlap each other at right angles to that direction. As a result of this there is no need for additional deflection rolls which results in a particularly simple and compact arrangement.
A further advantageous measure can be that the two lowest deflection rolls of the harp are capable of being driven. This makes it possible to pull the outermost web of the packet and thereby increase its tension. The specified measures therefore permit comparatively large lapping angles to be used for expelling the air such that even in difficult operating situations the air is removed in a particularly reliable manner.
Other advantageous developments and expedient developments of the superior measures of the present invention are provided in the following description of an exemplary embodiment as seen in the drawing.